1. Field of the Invention
Embodiments of the invention relate to low voltage drive single chip igniters, and to internal combustion engine ignition devices that include single chip igniters.
2. Description of Related Art
FIG. 8 is a main portion configuration diagram of an internal combustion engine ignition device 500 in which is mounted a heretofore known single chip igniter 501.
The internal combustion engine ignition device 500 is configured mainly of the single chip igniter 501, an ignition coil 502, a spark plug 503, a battery 504, and an engine control unit (ECU) 505. Of the reference signs in the diagram, 75, 76, and 77 are a collector terminal, a gate terminal, and an emitter terminal of the single chip igniter 501. Also, 51 is an IGBT including a sense IGBT, and 56 is a sense resistor.
FIG. 9 is a main portion circuit diagram of the heretofore known single chip igniter 501 mounted in the internal combustion engine ignition device 500 shown in FIG. 8. The single chip igniter 501 shown here is one example.
The single chip igniter 501 is configured of the IGBT 51, a first MOSFET 63, a second MOSFET 66, a current limiter circuit 57, an overheat detector circuit 60, a Zener diode 69, a resistor 72, the collector terminal 75, the gate terminal 76, and the emitter terminal 77. A collector 52 of the IGBT 51 is connected to the collector terminal 75, and an emitter 54 is connected to the emitter terminal 77. A sense emitter 55 of the IGBT 51 is connected to one end of the sense resistor 56, the other end of the sense resistor 56 is connected to ground wiring 74, and the ground wiring 74 is connected to the emitter terminal 77, which is a ground potential 78. A gate 53 of the IGBT 51 is connected via gate wiring 73 to the gate terminal 76. Each of the current limiter circuit 57, overheat detector circuit 60, first MOSFET 63, second MOSFET 66, Zener diode 69, and resistor 72 is connected between the gate wiring 73 and ground wiring 74. The overheat detector circuit 60 is configured of a MOSFET (A), a diode (B), and an inverter circuit (C), as shown in the diagram. Also, as well as the previously mentioned parts, a speed-up diode (D) for speeding up the turning off of the IGBT 51 is connected between the cathode of the Zener diode 69 and the source of the second MOSFET 66, and a Zener diode (F) for surge protection is connected between the collector 52 and gate 53. Also, surge protection resistors (E) are inserted in the gate wiring 73 between the resistor 72 and Zener diode 69, and between the high potential side of the current limiter circuit 57 and the drain of the second MOSFET 66. Each region is formed on one semiconductor substrate 81.
One end of the sense resistor 56 and a gate 64 of the first MOSFET 63 are connected to the current limiter circuit 57, while a gate 67 of the second MOSFET 66 is connected to the overheat detector circuit 60. The output voltage of the ECU 505 is input into the gate terminal 76 as the gate voltage of the IGBT 51. The gate voltage is supplied via the gate wiring 73 to the current limiter circuit 57 and overheat detector circuit 60, becoming a power supply voltage that drives the circuits 57 and 60.
The IGBT 51, first and second MOSFETs 63 and 66, current limiter circuit 57, overheat detector circuit 60, resistor 72, Zener diode 69, collector terminal 75, emitter terminal 77, and gate terminal 76 are formed on the same semiconductor substrate 81, thereby configuring the single chip igniter 501. The current limiter circuit 57 is formed of an operational amplifier configured of a three-stage n-type MOS. Also, the Zener diode 69 and resistor 72 are surge protection elements that suppress surge voltage entering from the gate terminal 76.
Also, the minimum operating voltage of the single chip igniter 501 is 3.5V, while the minimum operating voltage of each of the IGBT 51, current limiter circuit 57, and overheat detector circuit 60 configuring the single chip igniter 501 is 3.5V or less. Herein, the minimum operating voltage of the IGBT 51 indicates the gate threshold voltage of the IGBT 51. Also, the voltage value “3.5V” is the minimum voltage value of an ECU signal giving an operation command to the single chip igniter.
FIG. 10 is an external view of the single chip igniter 501 of FIG. 9. A chip (the semiconductor substrate 81) mounted on a lead frame die 80 (connected to a collector terminal C, which is one of external lead-out terminals 82) and external lead-out terminals 82 (a gate terminal G and an emitter terminal E) are connected with bonding wire 83, and packaged using mold resin 84.
Next, a description will be given of an operation of the internal combustion engine ignition device 500 shown in FIG. 8.
When an output signal from the ECU 505 is input as an input signal (IGBT gate signal) into the gate terminal 76 of the single chip igniter 501, the input signal is input via the gate wiring 73 into the gate of the IGBT 51, and the IGBT 51 is turned on. On the IGBT 51 being turned on, current flows from the positive electrode of the battery 504 via the ignition coil 502 and IGBT 51 to the emitter terminal 77, which is at ground potential.
Meanwhile, when the output signal from the ECU 505 stops, the IGBT 51 is turned off. The instant the IGBT 51 is turned off, energy accumulated in the ignition coil 502 is released, a high voltage is generated in the ignition coil 502, and the spark plug 503 ignites. Subsequently, when the energy accumulated in the ignition coil 502 is dissipated, the arc of the spark plug 503 is extinguished. By this operation being repeated, the internal combustion engine ignition device 500 continues to operate. Next, a description will be given using FIG. 9.
When an overcurrent flows through the IGBT 51, voltage is generated in the sense resistor 56 by a sense current flowing through the sense emitter 55 and sense resistor 56. The voltage is transmitted to the current limiter circuit 57, and the current limiter circuit 57 operates. A gate signal is sent from the current limiter circuit 57 to the first MOSFET 63, and the first MOSFET 63 is turned on. On the first MOSFET 63 being turned on, the gate voltage of the IGBT 51 is squeezed and decreases. When the gate voltage of the IGBT 51 decreases, dropping to or below the gate threshold voltage of the IGBT 51, the IGBT 51 is turned off, the overcurrent is cut off, and the IGBT 51 is protected.
Meanwhile, when the IGBT 51 overheats, the overheat detector circuit 60 operates and the IGBT 51 is turned off, in the same way as when there is an overcurrent. By the IGBT 51 being turned off, the main current flowing through the IGBT 51 is cut off, and the IGBT 51 is protected. When the IGBT 51 overheats, the forward voltage drop value of an unshown temperature detection p-n diode formed in the IGBT 51 decreases. The forward voltage drop value (voltage) is input into the overheat detector circuit 60 and, at the point at which the forward voltage drop value drops to or below a limit value, a turn-on signal is sent from the overheat detector circuit 60 to the gate of the second MOSFET 66, and the second MOSFET 66 is turned on. The subsequent operation is the same as in the case of the current limiter circuit 57. The overheat detector circuit 60 and current limiter circuit 57 both function as control circuits that control the gate voltage of the IGBT 51.
As the single chip igniter 501 is used in the internal combustion engine ignition device 500, the usage environment is extremely harsh. To give a specific description, the IGBT 51 should not destruct even when a surge voltage of 30 kV is applied between the collector terminal 75 and emitter terminal 77, and the IGBT 51 should operate normally (this means that a parasitic element does not operate) in a temperature range of, for example, −55° C. to 205° C. In order for the single chip igniter 501 to operate normally even under these harsh conditions, the current limiter circuit 57 and overheat detector circuit 60 are configured of only an n-type MOS. This is because the process is complex when a p-type MOS and n-type MOS exist together, leading to a rise in cost. Also, when adopting a hybrid circuit (a complementary circuit, or the like) of a p-type MOS and n-type MOS, a parasitic element is formed between the two, and a parasitic operation (a malfunction) is liable to occur.
Japanese Patent No. 3,192,074 discloses a single chip igniter in an internal combustion engine ignition device including a switching element that controls the conduction and cutting off of a primary current flowing through an ignition coil in response to an ignition control signal output from an internal combustion engine electronic control device, and a current limiter circuit that limits the current flowing through the switching element, the switching element being configured of an insulated gate bipolar transistor, wherein the current limiter circuit is configured of a self-isolating n-type MOS transistor, and the insulated gate bipolar transistor and self-isolating n-type MOS transistor are formed on the same semiconductor substrate, thereby forming a single chip. That is, Japanese Patent No. 3,192,074 discloses a single chip igniter wherein a current limiter circuit is configured of a self-isolating n-type MOS transistor (an n-type MOS) and formed on the same semiconductor substrate as an IGBT.
Also, Japanese Patent No. 3,216,972 discloses a single chip igniter in an internal combustion engine ignition device that includes a first IGBT, and controls the conduction and cutting off of a primary current flowing through a primary coil with the first IGBT in response to an ignition control signal, thereby generating voltage on a secondary side thereof, the single chip igniter including a second IGBT provided in parallel with the first IGBT, a current detector circuit that detects the current of the second IGBT, a current limiter circuit that controls the gate voltages of the first and second IGBTs in accordance with the current value detected by the current detector circuit, thereby limiting the primary current to a setting value, and a thermal cut-off circuit that forcibly cuts off the conduction of the current flowing through the primary coil when a problem occurs, wherein the circuits are configured collected on one chip.
Also, in JP-A-2010-45141, an IGBT that intermits a low voltage current flowing through a primary side coil, a fixed voltage circuit between an external gate terminal and an external collector terminal, and a protection Zener diode are included in an internal combustion engine ignition device. The fixed voltage circuit supplies to the IGBT a certain gate voltage such that a saturated current value of the IGBT reaches a predetermined limit current value. The IGBT is such that the saturated current value is in the range of the limit current value of a semiconductor device. A plurality of depression MOSFETs connected in parallel and a Zener diode are connected in series in the fixed voltage circuit. A selector switch is connected to each depression MOSFET, and all the selector switches are connected to a selector circuit. Further, when shipping from the factory, voltage fluctuation caused by electrical characteristics in the semiconductor device manufacture is adjusted by carrying out a turning on and off of the selector switches using the selector circuit. By so doing, oscillation in the waveform of the current flowing through the IGBT is suppressed. JP-A-2010-45141 discloses that a reduction in the overall size of the semiconductor device is achieved, and cost is reduced. A trench gate IGBT and a planar gate IGBT are described as the semiconductor device used here.
The collector terminal 75 of the single chip igniter 501 is connected to the battery 504 via an internal resistor of the ignition coil 502, and the emitter terminal 77 is connected to, for example, an engine room chassis, which is at the ground potential 78. Because of this, the potentials of the terminals 75 and 77 are comparatively stable.
As opposed to this, the potential of the gate terminal 76 is a low potential determined by the low output voltage (5V) of the ECU 505 and the small gate capacitance of the IGBT 51. Also, as an ignition pulse (several tens of kilovolts) is generated in the immediate vicinity of the single chip igniter 501, there is concern that the single chip igniter 501 will malfunction due to noise, and the output voltage of the ECU 505 may decrease due to noise. Furthermore, when the IGBT 51 is conductive, voltage is generated by the product of the resistance of ground wiring, such as a harness, and the conduction current, and it may happen that the ground potential 78 of the single chip igniter 501 rises (the ground floats) due to the voltage. Specifically, for example, when the rated conduction current of the IGBT is 10 A, and the resistance of a harness type of ground wiring between the IGBT and ECU and the ground is, on the high side, 0.1Ω, the product of the resistance and the conduction current reaches 1V, and this 1V is the rise (ground floating) of the ground potential. When ground floating occurs, it may happen that the voltage (gate signal voltage) between the gate terminal 76 of the single chip igniter 501 and the emitter terminal 77, which is at the ground potential 78, drops to 3.5V or less, and the operation of the single chip igniter 501 becomes unstable.
Next, a description will be given of heretofore known technology for combating voltage drop.
FIG. 11 is a main portion configuration diagram of a hybrid igniter 600. The hybrid igniter 600 includes an IGBT 51a and an IGBT drive circuit 90, and a current limiter circuit, an overheat detector circuit, and a sense resistor 56a are included in the IGBT drive circuit 90. Each of these parts is fixed on a printed substrate 91, a ceramic substrate, or the like.
It may happen that the output voltage from the ECU 505 drops below 3.5V due to noise, or the like, or that ground floating occurs, and the voltage between the gate and emitter of the IGBT 51a drops below 3.5V. At this time, it is necessary to compensate for the voltage drop, and constantly maintain the voltage between the gate and emitter of the IGBT 51a at or above 3.5V. When depressing noise is superimposed on the input voltage (gate voltage) input from the ECU 505, or when ground floating occurs, the IGBT drive circuit 90 has a function of compensating for the noise or the floating, and transmitting the regular gate voltage to the gate of the IGBT 51a. 
The configuration of the hybrid igniter 600 of FIG. 11 is such that it is necessary for a large number of individual parts to be mounted on the printed substrate 91, or the like, and the number of parts increases. Because of this, the external dimensions increase, and the manufacturing cost increases.
Also, in Japanese Patent No. 3,192,074, Japanese Patent No. 3,216,972, and JP-A-2010-45141, no description is found suggesting a measure for reducing the operating voltage of a single chip igniter used in an internal combustion engine ignition device, which is the point of the invention. Thus, as is described above, there is a need in the art for an improved igniter.